A fiber-reinforced composite material in which reinforced fibers such as a carbon fiber, a glass fiber, and an aramid fiber and a matrix resin such as an epoxy resin are combined has been developed, and regarding such reinforced fibers, by laminating thin spread fiber sheets aligned in one direction in multiple directions for use, reliable composite material moldings with high strength can be obtained. Also, in view of advantages of recyclability, short time moldability, improvement in impact resistance of the moldings and the like, use of a composite material molding using a thermoplastic resin such as polyamide 6 resin, polyether imide resin, polyetheretherketone resin and the like for the matrix resin is expected to increase.
Recently, a carbon fiber composite material has drawn a marked attention as materials for aircrafts and vehicles. There are various carbon fibers, and major carbon fibers include a carbon fiber called a general-purpose carbon fiber of a type having a tensile modulus of approximately 24 ton/mm2 and a single-fiber diameter of approximately 7 μm used for industrial applications and sport applications and a carbon fiber called high-strength and moderate-elasticity carbon fiber having a tensile modulus of approximately 30 ton/mm2 and a single-fiber diameter of approximately 5 μm used for aircraft application.
A plurality of the carbon fibers is bundled and sold as a carbon fiber bundle, and the number of fibers is also varied. From the viewpoint of price, quality of the product (straightness of the fiber, aligned state of the fibers and the like), and ease of handling, those with the number of fibers of 12000 and 15000 (fineness of approximately 800 to 1100 g/1000 m) are mainly used for the general-purpose carbon fiber bundle and those with the number of fibers of 12000 and 24000 (fineness of approximately 400 to 1000 g/1000 m) for the high-strength and moderate-elasticity carbon fiber bundle.
The general-purpose carbon fiber bundles include a type in which the number of fibers is increased in order to reduce the price, and those with the number of fibers of 24000 (fineness of approximately 1600 g/1000 m) and 48000 (fineness of approximately 3200 g/1000 m) or more are sold in the market. Since these fiber bundles have large fineness, they are also called large-fineness carbon fiber bundles. However, the carbon fiber bundle having an increased number of fibers has a defect that the larger the number of fibers becomes, the more meandering and tangling of fibers occur.
For development of a thin sheet and improvement of impregnating performance of a highly viscous resin such as a thermoplastic resin, a spreading process of making the fiber bundle wide and thin is needed. Particularly, the spreading process is important for a fiber bundle having an increased number of fibers. As a spreading technology, Patent Document 1, for example, discloses a manufacturing method of a multifilament spread sheet in which an airflow is made to pass several times in a direction crossing the multifilament while the multifilament is fed from a fiber feeding portion to a take-up portion so as to bend the multifilament in an arc shape in the leeward direction so that filaments forming the multifilament is unwound and spread in the width direction. Also, in Patent Document 2, a spreading device is described which includes a feeding-out roll around which a fiber assembly is wound, a spread portion which spreads the fiber assembly fed out of this feeding-out roll by causing a fluid to flow in a direction orthogonal to the moving direction of the fiber assembly, and a take-up roll which takes-up a spread sheet having been spread in the spread portion, and in which spread portions are disposed in plural stages in the moving direction. Also, in Patent Document 3, a spreading device is described in which a fiber bundle is pulled out of each of a plurality of fiber feeding bodies and supplied and the supplied fiber bundle is made to run through an air flow in a plurality of fluid flowing portions so that the fiber bundle is spread in the width direction while being bent by the action of the airflow.